Length change, hydration heat, setting time and compressive strength of OPC were measured by adding KCl and replacing limestone powder so as to examine the influence of limestone powder on hydration of the OPC contained much chloride. In general, the chloride modified cement was high in heat of hydration, short in its setting time, low in its fluidity and low in its strength at 28 days due to the sudden hydration in its initial stage. As a result of the experiment, it has been demonstrated that heat of hydration, became low as one replaced limestone powder to the chloride modified cement, and the fluidity and shrinkage rate of mortar decreased without change in setting time; furthermore, the compressive strength at 28 days was improved.